The present invention relates to a wheel assembly for use in vehicles such as a scissor lift and more particularly relates to a modular wheel assembly which includes a wound field DC motor mounted within the hub of the assembly and directly driving the wheel via an intermediate planetary gear mechanism.
In the past, the wheels of such vehicles have been driven primarily by external hydraulic motor systems connected to the wheels by intermediate adapter components. These systems tend to be mechanically complicated and expensive and utilize space on the vehicle which could be more efficiently occupied by other components. Various type wheel assemblies which include conventional AC or DC electric motors and planetary speed reducer units to drive the wheel have also been previously proposed, but those assemblies have not been widely accepted commercially. For example, prior conventional wound field DC motors consisted of thick machine frames drilled with holes to mount laminated field pole pieces and end housings. The poles were laminated to reduce eddy current losses and were punched from electrical grade silicon steel. The pole pieces were then stacked and welded on both sides. To bolt the pole pieces into the frame they had to be drilled and tapped. Installing field coils around each pole piece and bolting them into the frame completed the assembly. The result was a large, heavy, very costly, labor intensive motor which did not lend itself for application for use in a wheel assembly.
The industry recognizes the desirability of utilizing such modular wheel drives, but requires that the components of the assembly, particularly the parts of the DC motor, be minimized in number, size, and weight to provide a cost effective, compact design which is capable of satisfying the required horsepower and torque requirements of the vehicle.
The invention as described hereinbelow was developed to satisfy that need.